Two polyubiquitin clones have been isolated from a rat brain cDNA library. Clone 22B1 contained four repetitive ubiquitin in tandem. Clone 19A2 coded ten complete repetitive ubiquitin followed by the first 20 amino acids of the previous repetitive ubiquitin and a distinct peptide. These clones were rat homologues for human UbB and UbC gene families, respectively. 1.2 kb UbB transcript, as well as 2.8 kb and 3.2 kb UbC transcripts, were widely expressed in the various rat tissues.